> For the complete documentation index, see [llms.txt](https://horizongames.gitbook.io/actorio/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://horizongames.gitbook.io/actorio/usage/actor-i-o-subsystem.md).

# Actor I/O Subsystem

The I/O subsystem is a context handler for the I/O system that is unique per game world. It stores the current `ActionExecutionContext`, exposes a list of natively supported I/O events and functions, and a list of globally available [**Named Arguments**](/actorio/usage/named-arguments.md).

There must always be one I/O subsystem available both at runtime, and in Unreal Editor. Unless specified otherwise, the `ActorIOSubsystemBase` class will be used.

### Customizing the I/O Subsystem

1. Create a new blueprint (or C++ class) from the `ActorIOSubsystemBase` class.
2. Go to **Edit -> Project Settings -> Actor I/O**.
3. Set the subsystem class to your own, and re-open the level.

<figure><img src="/files/CWVUw7gbnmCB2gGBfPzR" alt=""><figcaption></figcaption></figure>

{% hint style="warning" %}
Changing the I/O Subsystem class **requires a level reload** to fully take effect!
{% endhint %}


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